Effect of Bone Morphogenetic Proteins on Dental Pulp Differentiation

Bone morphogenetic proteins (BMPs) are known to regulate primary tooth formation (odontogenesis) and subsequent mineralized extracellular matrix (dentin and enamel). In particular, odontoblasts that secrete the dentin matrix have been shown to be responsive to several BMPs in an autocrine and paracrine manner. However, the ability of BMPs to regulate differentiation of the precursor ectomesenchymal dental pulp cells towards odontoblasts remains unanswered. Objectives: To assess and compare the inductive potential of BMP-2, BMP-4, and BMP-7 to promote dental pulp cytodifferentation into functional odontoblasts in vitro. Methods: Immortalized mouse dental pulp (MD10D3, MD10A11) and odontoblast (MO6-G3) cell lines were cultured in alpha-MEM supplemented with BMP-2, BMP-4, or BMP-7 (0, 100, 200ng/ml). Treated and non-treated cells were analyzed for cell proliferation (MTT assay) and alkaline phosphatase (ALP) activity (in situ histochemistry) at various time points. Parallel cell cultures were used to isolate total RNA that was converted to cDNA for quantitative real-time PCR (qRT-PCR) analysis of BMPs, their receptors and various dentin matrix proteins. Results: In general, BMP treatment of the pulp cell lines resulted in slight modulation of cell proliferation and an induction of ALP activity. At ten days, ALP staining of MD10A11 cells was enhanced in all BMP treatment groups as compared to non-treated. In the odontoblast MO6-G3 cells, cell proliferation and ALP activity was not significantly altered by BMP treatment. Endogenous expression of BMPs, their receptors and production of dentin matrix was confirmed and quantified with qRT-PCR. Comparison between treated and non-treated cells revealed that BMP signaling does alter the gene expression profiles of the cell lines tested. Conclusion: These studies suggest that BMP proteins promote the terminal cytodifferentiation of dental pulp cells towards the odontoblast lineage and regulate production of the dentin matrix. Support: UAB-IOHR/NIDCR-T32DE017607.